IMP
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Post by IMP on Aug 24, 2011 18:24:15 GMT -5
This thread is for everything about Mopar rearends This should be helpful.
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dm440c
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derby drivers against drama- there's no crying in demo derby!
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Post by dm440c on Aug 25, 2011 12:36:18 GMT -5
8-3/4 info 8-3/4 is a bolt in axle design. Dropout center section (front load) with 10 bolts is the 8-3/4. If you see a bolt-on cover in the rear it is not an 8-3/4. 1964 & older "big nut" axles use a keyway to joint the axle shaft to the drive hub. These can be a real pain to deal with and are suspect for durability. The 1965 & newer one piece shafts are preferred by most derbiers big nut one piece all 8-3/4 center sections are interchangeable with all tubes and all shafts open differential: cone type Sure Grip clutch type Sure Grip when welding the open diffs, weld the spider gears together and use old bolts as filler. DO NOT weld the center pin or you will find it very difficult to set the axle end play/ thrust I buy used gears from drag racers at swap meets. I'm not a fan of spools.... just welded rears. Brake parts can usually be interchanged from other axles, when I am setting up a new 8-3/4 I usually transfer all of the brake parts from a 70's model C clip axle (8-1/4 or 9-1/4) There were many different widths of 8-3/4 axles depending on model and year. The axle shaft length has to be correct for the tube length 3 wheel bolt patterns: 5 on 5.5" is 1966 & older Imperial; 5 on 5.0" is 67-73 Imperial, everything else is 5 on 4.5" 3 most common center section castings are 741, 742, and 489. Gearsets are particular to the casting 8-3/4 was in wide use up until 1969, after that they were slowly phased out and rarely seen past 1974
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Post by XtremeMopar#307 on Aug 26, 2011 18:56:10 GMT -5
aint ever seen much on posi... my 78 newport, thought it had a 8 1/4, its got a 9 1/4, but on the back cover someone painted posi with a white marker, is factory posi good or bad for derby use? just aint seen much on it
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Post by anaconda on Aug 26, 2011 23:39:20 GMT -5
agree with dm440c as far as spools to a certain extent. If not setup right with green bearings forget it, it will not work. You sacrifice things to gain others with full spool. However axels stock can be broken, mopar more than 9 inch ford.
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dm440c
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Post by dm440c on Aug 29, 2011 10:50:45 GMT -5
in my experience it seems to have a lot to do with setup and driving style. Our crew has never had much trouble from broken 8-3/4 axle shafts but 9 inch differentials and gearsets seem to be made from peanut butter. As for the "posi" question you'll have to ask it in the GM section, that's where they discuss "Positraction" limited slip differentials. Here in the Mopar world we deal with "Sure Grip" limited slip differentials But seriously, the pictures I showed above look basically the same in a 7-1/4, 8-1/4 or a 9-1/4. Pop the cover off and look at the diff to see if it is open or limited slip.
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Post by XtremeMopar#307 on Aug 29, 2011 19:00:52 GMT -5
ill be sure to do that this weekend.... thanks
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Post by dpolara on Sept 11, 2011 13:30:41 GMT -5
Will the yoke off of a 8 1/4 reared fit on a 8 3/4?
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dm440c
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derby drivers against drama- there's no crying in demo derby!
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Post by dm440c on Sept 12, 2011 13:07:30 GMT -5
Will the yoke off of a 8 1/4 reared fit on a 8 3/4? I'm having a bit of a brain fart on that one, I know a 9-1/4 yoke will fit on an 8-3/4 but I think the 8-1/4 is smaller than those other two. Not 100% on that but I think I have it right.
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2old4this
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Post by 2old4this on Sept 12, 2011 13:33:19 GMT -5
8-3/4 info 8-3/4 is a bolt in axle design. Dropout center section (front load) with 10 bolts is the 8-3/4. If you see a bolt-on cover in the rear it is not an 8-3/4. 1964 & older "big nut" axles use a keyway to joint the axle shaft to the drive hub. These can be a real pain to deal with and are suspect for durability. The 1965 & newer one piece shafts are preferred by most derbiers big nut one piece all 8-3/4 center sections are interchangeable with all tubes and all shafts open differential: cone type Sure Grip clutch type Sure Grip when welding the open diffs, weld the spider gears together and use old bolts as filler. DO NOT weld the center pin or you will find it very difficult to set the axle end play/ thrust I buy used gears from drag racers at swap meets. I'm not a fan of spools.... just welded rears. Brake parts can usually be interchanged from other axles, when I am setting up a new 8-3/4 I usually transfer all of the brake parts from a 70's model C clip axle (8-1/4 or 9-1/4) There were many different widths of 8-3/4 axles depending on model and year. The axle shaft length has to be correct for the tube length 3 wheel bolt patterns: 5 on 5.5" is 1966 & older Imperial; 5 on 5.0" is 67-73 Imperial, everything else is 5 on 4.5" 3 most common center section castings are 741, 742, and 489. Gearsets are particular to the casting 8-3/4 was in wide use up until 1969, after that they were slowly phased out and rarely seen past 1974 Mr. dm440c, thanks for sharing and posting pics with your info. I would like to know is the sure grip center section that which would be compared to a posi-trac?
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Post by XtremeMopar#307 on Sept 12, 2011 18:40:35 GMT -5
yes it is, dont ask about posi in here LOL, i found that out
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Post by nick1860 on Sept 12, 2011 19:07:08 GMT -5
Posi is a four letter word around here its a GM thing
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2old4this
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We may not have all the answers but, we're big enough to be questionable.
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Post by 2old4this on Sept 12, 2011 19:37:51 GMT -5
yes it is, dont ask about posi in here LOL, i found that out I was careful not to call the sure grip the other name. I see that dm440c prefers a welded open diff. I was wondering if there is a weak link in the clutch sure grip which would lead him to that preference?
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nevadapitbull
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Post by nevadapitbull on Sept 12, 2011 21:29:35 GMT -5
when i weld my gears i allow them to cool naturally for an hr or so then i fill them up with old motor oil so the steel can absorb the oil. i wont ever run a spool, sure grip, or posi because they have more parts to break. the spools just look dainty to me. i can afford open gears and they're plentiful. just my opinion
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n8
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Post by n8 on Sept 12, 2011 21:51:40 GMT -5
yes it is, dont ask about posi in here LOL, i found that out I was careful not to call the sure grip the other name. I see that dm440c prefers a welded open diff. I was wondering if there is a weak link in the clutch sure grip which would lead him to that preference? If you have ever priced out the cost of a center section with a sure grip in it already, or just the sure grip unit itself, you would have your answer. Any sure grip unit I have found has been above the cost of a spool, or in some cases, more than the cost of better gears and a spool. He may have another reason but my guess is cost and simplicity.
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Post by XtremeMopar#307 on Sept 12, 2011 22:08:23 GMT -5
my 78 newport has a factory 9 1/4 sure grip in it...
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